Vehicles are typically characterized by one of two types of construction, namely body-on-frame construction and unibody construction, which is also sometimes referred to as body-frame integral construction. As understood by those skilled in the art, the vehicle body and the vehicle frame are the same in unibody construction; that is, the body forms the frame. With body-on-frame construction, a body is mounted to a separate chassis frame.
Prior art chassis frames are referred to as “ladder frames” because they comprise two longitudinally-oriented rails that extend substantially the length of the body to which the frame is attached, and two or more transversely-oriented cross members that rigidly interconnect the two rails.